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3.2b) Effect of varying inter-crestal spacing
Below we consider how the shedding frequency is affected by
changes in L, the inter-crestal spacing. For this study we chose
a flow velocity of 0.43m/s (where the Coanda-flapping events are
most strong) and varied L in intervals of 0. 5L 0 (half
wavelength) , from L 0 to 3L 0 . We could not visualise the oncoming
flow vortices at this velocity but continued because the Coandaflapping
events are certainly stronger and easily visualisable.
The interval distribution for Coanda-flapping events here,
recorded as in section 3.2a, is shown in figure 8 for each value
of L. Of major interest is the change in modal location for
L=3L 0 and broadening of the distribution which is discussed
further below. It is clear that our bin size is too large at Is
so we revert to the raw data and plot the interval data for L=L 0
sorted in ascending numerical order against the cumulative sum
of the intervals in figure 9. The reason for following this
procedure was explained in section 2.2. Thus, for L=L 0 we
retrieve a modal value between 0.9 and 1.3s (ie about l.ls)
corresponding to the minimum point on figure 9 and the gradient
plot in figure 10. The limits were defined arbitrarily as any
gradient region below 0.02 and any higher or lower limit simply
changes the band width. The same region corresponds to the first
line in the top left-hand corner of figure 11. The number (32%)
above the line corresponds to the percentage of all the measured
intervals that fell within this range (ie 0.9 to 1.3s) whereas
the figure in italics below the line is the percentage of events
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